1. Field of the Invention
The present invention relates to an objective lens for an optical pickup, and an optical pickup device loaded with the objective lens; and more particularly to a resin objective lens which converges laser light in a blue wavelength region on a disc, and an optical pickup device loaded with the objective lens.
2. Disclosure of Related Art
In recent years, a resin objective lens is loaded in an optical pickup device. Since the resin objective lens is lightweight as compared with a glass objective lens, it is possible to enhance the driving response of the objective lens. Further, since the resin objective lens is inexpensive, it is possible to reduce the cost of an apparatus.
Japanese Unexamined Patent Publication No. 2001-324673 discloses an objective lens having a numerical aperture of 0.75 or more, and suitable for use of laser light having a wavelength of or about 400 nm. Such an objective lens is designed to satisfy a condition: 1.1≦d1/f≦3 (where d1 is an on-axis lens thickness, and f is a focal length).
However, if laser light of a wavelength of or about 400 nm is entered into a resin objective lens, the objective lens may be degraded by the laser light. In particular, a resin material to be used for an objective lens is likely to absorb light in a wavelength region of or about 400 nm. As a result, the objective lens may be degraded, which may lower the optical characteristics such as light transmittance.